Various obstructive airway diseases have some reversible component. Examples include COPD and asthma. There are an estimated 10 million Americans afflicted with Asthma. Asthma is a disease in which bronchoconstriction, excessive mucus production, and inflammation and swelling of airways occur, causing widespread but variable airflow obstruction thereby making it difficult for the asthma sufferer to breathe. Asthma is a chronic disorder, primarily characterized by persistent airway inflammation. Asthma is further characterized by acute episodes of additional airway narrowing via contraction of hyper-responsive airway smooth muscle.
Reversible aspects of obstructive pulmonary disease generally include excessive mucus production in the bronchial tree. Usually, there is a general increase in bulk (hypertrophy) of the large bronchi and chronic inflammatory changes in the small airways. Excessive amounts of mucus are found in the airways and semisolid plugs of mucus may occlude some small bronchi. Also, the small airways are narrowed and show inflammatory changes. Reversible aspects include partial airway occlusion by excess secretions and airway narrowing secondary to smooth muscle contraction, bronchial wall edema and inflammation of the airways.
In asthma, chronic inflammatory processes in the airway play a central role in increasing the resistance to airflow within the lungs. Many cells and cellular elements are involved in the inflammatory process, particularly mast cells, eosinophils T lymphocytes, neutrophils, epithelial cells, and even airway smooth muscle itself. The reactions of these cells result in an associated increase in the existing sensitivity and hyper-responsiveness of the airway smooth muscle cells that line the airways to the particular stimuli involved.
The chronic nature of asthma can also lead to remodeling of the airway wall (i.e., structural changes such as thickening or edema) which can further affect the function of the airway wall and influence airway hyper-responsiveness. Other physiologic changes associated with asthma include excess mucus production, and if the asthma is severe, mucus plugging, as well as ongoing epithelial denudation and repair. Epithelial denudation exposes the underlying tissue to substances that would not normally come in contact with them, further reinforcing the cycle of cellular damage and inflammatory response.
In susceptible individuals, asthma symptoms include recurrent episodes of shortness of breath (dyspnea), wheezing, chest tightness, and cough. Currently, asthma is managed by a combination of stimulus avoidance and pharmacology.
Stimulus avoidance is accomplished via systematic identification and minimization of contact with each type of stimuli. It may, however, be impractical and not always helpful to avoid all potential stimuli.
Pharmacological management of asthma includes: (1) long term control through use of anti-inflammatories and long-acting bronchodilators and (2) short term management of acute exacerbations through use of short-acting bronchodilators. Both of these approaches require repeated and regular use of the prescribed drugs. High doses of corticosteroid anti-inflammatory drugs can have serious side effects that require careful management. In addition, some patients are resistant to steroid treatment. The difficulty involved in patient compliance with pharmacologic management and the difficulty of avoiding stimulus that triggers asthma are common barriers to successful asthma management. Current management techniques are thus neither completely successful nor free from side effects. Accordingly, it would be desirable to provide a system and method which improves airflow without the need for patient compliance.
Various energy delivering systems have been developed to intraluminally treat anatomical structures and lumen other than the lung airways. Unfortunately, the systems which are useful in treating such structures are generally not helpful in developing techniques to treat the lung airways because the lung airways are markedly different than other tissue structures. For example, lung airways are particularly heterogeneous. Variations in lung tissue structure occur for a number of reasons such as: the branching pattern of the tracheobronchial tree leads to local variation in the size and presence of airways; the vasculature of the lungs is a similar distributed network causing variation in size and presence of blood vessels; within the airways are variable amounts of differing structures such as cartilage, airway smooth muscle, and mucus glands and ducts; and energy delivery may also be influenced differently at the periphery, near the outer surface of a lung lobe, than in the central portion.
Lung airways also include a number of protruding folds. Other tissue structures such as blood vessels typically do not have the folds found in airways. Airways contain mucous and air whereas other structures contain different substances. The tissue chemistry between various lumens and airways is also different. In view of these differences, it is not surprising that conventional energy delivering systems cannot be universally applied to treat all tissue structures. Moreover, power shut-offs and other safety mechanisms must be precisely tailored to specific tissue so that the tissue is not harmed by application of excess energy.
Accordingly, an intraluminal RF energy delivering system that is capable of safely delivering RF energy to lung airways is desired. In particular, a system which is capable of controlling the temperature when treating an airway of an asthma or COPD patient is desired. It is also desirable to provide a system having built-in safeguards that shut the power off thereby preventing damage to the subject tissue or collateral tissue.